1. Field of the Invention
The invention relates to a control method, and more particularly to a control method for a memory.
2. Description of the Related Art
Flash memories comprise NOR flash memories and NAND flash memories. The read speed of the NOR flash memory is faster than the NAND flash memory. But, the capacity of the NOR flash memory is smaller. The NAND flash memory possesses favorable advantages of having a smaller volume, lower power consumption, and larger capacity. Thus, NAND flash memories are widely used in different fields such as fields for mobile products. The NAND flash memory comprises various storage units. When the storage unit only stores a single bit, the storage unit is referred to as a single level cell (SLC). When the storage unit can store various bits, the storage unit is referred to as a multi level cell (MLC). The read speed and the write speed of the NAND flash memory are slower and the reliability of the NAND flash memory is lower than the NOR flash memory.
FIG. 1A is a flowchart of a conventional read method for an NAND flash memory. The NAND flash memory comprises various multi level cells. As shown in FIG. 1A, an external device issues a read command to the NAND flash memory (step 110). When the NAND flash memory receives the read command, data is provisionally stored in an internal cache (step 120). After all data are stored in the internal cache, the external device reads the data stored in the internal cache (step 130).
FIG. 1B is a timing diagram of reading a multi level cell. Assuming the capacity of the NAND flash memory is (4096+128) bytes and each storage unit stores two bits, when an external device desires to read the data stored in the NAND flash memory, the NAND flash memory requires 175 ns to receive the read command and then requires 50 us to store data in the internal cache. After the all data are stored in the internal cache, the external device requires 105.6 us to receive data stored in the internal cache. As described previously, the read speed and the write speed of the NAND flash memory are slower because the NAND flash memory stores various bits. Thus, to improve performance of the NAND flash memory, a control method is required to raise the read speed and the write speed.